1. Field of the Invention
This invention relates to a frequency adjusting circuit for digitally adjusting the frequency of a time reference signal delivered from an oscillation circuit to a given value.
2. Description of the Prior Art
Heretofore, an analog system and a digital system have been proposed as a frequency adjusting system for a quartz oscillation circuit comprising a quartz oscillator as a reference oscillator. In general, the analog system makes use of a trimmer condenser connected to the outside of an input or output of the quartz oscillation circuit and the capacity of the trimmer condenser is changed so as to adjust the frequency of output pulses delivered from the quartz oscillation circuit. As a result, in electronic devices such as an electronic time piece which is required to be small in size, there arises an important problem how to make the trimmer condenser small in size so as to make the electronic time piece as a whole small in size. In addition, the trimmer condenser gradually changes its capacity after the lapse of time irrespective of the change in the number of oscillations of the quartz oscillator per se, and as a result, the oscillation frequency becomes changed. Moreover, the capacity of the trimmer condenser considerably influences the electric power consumed by the oscillation circuit. For to the above mentioned reasons, the number of oscillations inherent the quartz oscillator must lie within a very limited range for the purpose of causing the oscillation frequency of the oscillation circuit not to deviate from the frequency desired and of operating the oscillation circuit with the least possible electric power consumed.
The conventional frequency adjusting circuit has the drawback that in the case of measuring pitches every one second, for example, if the frequency adjusting value is large, the pitch becomes changed each second, thereby rendering the measurement difficult.